When the material within the lens capsule of the eye becomes clouded a cataracteous condition results thereby obstructing the passage of light. Two forms of surgery are presently used to correct this condition.
The first form of surgery is known as intracapsular cataract extraction by which the lens and entire capsule are removed intact. In order to accomplish this, the surgeon pulls the lens free from the zonules or suspensory ligaments which normally engage the periphery of the capsule. The entire lens and capsule with its content material intact are then removed.
The second form of surgery is known as extracapsular cataract extraction, which involves making an incision through the anterior surface of the lens capsule. The clouded cellular material of the lens is then removed through the incision by suction of phacoemulsification, without removing the entire capsule. The clear rear wall of the capsule, known as the posterior capsule surface, remains in place in the eye. The zonules and the peripheral portions of the anterior capsule surface, which are known as the anterior capsule flaps, also remain in place.
The trend in cataract surgery has been towards the latter or the extracapsular procedure, because of certain undesirable complications which may result from intracapsular surgery.
Both the intracapsular and extracapsular cataract extraction procedures eliminate the light blockage due to the cataract. However, the light that now enters the eye through the cornea and pupil is unfocused due to the removal of the natural lens of the eye. Focusing may be achieved by positioning a contact lens on the external surface of the cornea to the eye, and/or by the use of spectacles. Although such external lenses are generally satisfactory, there are disadvantages because when they are removed the patient effectively has virtually no sight. The preferred alternative is to implant an artificial intraocular lens (IOL) directly into the eye.
The entire area behind the lens is normally filled with a jelly-like material called the vitreous humor. Occasionally during intracapsular surgery, when the lens is removed intact, the vitreous humor comes up through the pupil and it may escape from the eye through the incision that was made in order to carry out the intracapsular extraction. This gives rise to adverse side effects.
Cystoid Macular Edema (CME) is another complication which occurs more frequently in intracapsular surgery. This is a swelling of the macula of the retina. It is believed that the swelling is caused by certain enzymes which are released from the iris and migrate through the vitreous humor and back to the macula. This is a serious complication. During extracapsular surgery, however, since the posterior capsule remains intact, the vitreous humor is prevented from getting into the anterior chamber of the eye. The incidence of cystoid macular edema or retinal detachment is markedly reduced with extracapsular surgery.
Accordingly, from the viewpoint of reducing post-surgical complications, extracapsular extraction is the presently preferred surgical procedure. The present invention provides an improved intraocular lens which is particularly advantageous for use in conjunction with extracapsular extractions. It can also be used in intracapsular extraction when place in the anterior chamber.
Harold Ridley was the first physician in the early 1950's to implant a posterior chamber lens into the eye. Ridley used a biconvex lens which was about the same shape, but was approximately 1 millimeter smaller in diameter than the human lens. The Ridley lens had a weight in air of 112 mg and, accordingly, represented an extremely heavy object to be implanted into the eye.
The usual prior art intraocular lens is rigid and is formed, for example, of an appropriate transparent plastic such as methyl methacrylate. However, U.S. Pat. No. 4,573,998 discloses an intraocular lens structure which comprises a deformable optical zone portion with prescribed memory characteristics. The optical zone portion of the lens described in the patent, may be deformed by rolling or folding to reduce the diameter of the optical zone so that the lens may be inserted into the eye through a relatively small incision, as compared with the incision required for the insertion of the rigid lenses. After insertion into the eye, the optical zone portion of the lens returns to its original configuration. The deformable lens described in the patent maybe formed to have its optical zone composed of one or more suitable flexible materials such as polyurethane elastomer, silicone elastomer, hydrogel polymer collagen compounds, organic or synthetic gel compounds and combinations thereof.
The use of a deformable intraocular lens during the surgical procedure has distinct advantages over the rigid intraocular lens, because the latter requires a relatively large incision in the ocular tissue. This leads to a relatively high complication rate, such as astigmatism, vitreous loss, retinal detachment, and cystoid macular edema. Accordingly, these disadvantages are overcome to a large extent by the use of the lens disclosed in the patent which requires a smaller incision for its insertion into the eye. The small incision also facilitates rapid physical and visual rehabilitation.
The lens of the present invention may be flexible, and it may be formed of any of the materials listed above. However, the lens of the present invention when made of flexible material represents a distinct advantage over the lens described in U.S. Pat. No. 4,573,998, in that it can be deformed into a much smaller diameter for insertion into the eye. Accordingly, the incision required for the insertion of the lens of the present invention is so small that suturing of the incision may not be required at the completion of the operation. Therefore there should be virtually no surgically induced astigmation.
The lens described in U.S. Pat. No. 4,573,998, like the human lens has biconvex configuration. This means that it must have a significant thickness in order to perform the required focusing function.
Another type of lens which overcomes many of the biconvex lens shortcomings, i.e. thickness, folding difficulties, longer incisions required, is the Fresnel lens, whose application to intraocular lenses is described in U.S. Pat. No. 4,673,406. Such a lens can be made sufficiently thin so that it may be inserted through a very small incision and if made of the appropriate material may unfold to its original shape after insertion.
Fresnel optics with the opposite side spherical are generally stiffer, as one might expect, and therefore resist bending or folding and generally require a larger incision for insertion. The combination of Fresnel surfaces on the front and back side has proven self-defeating in other applications. Therefore, it may be assumed that the same would happen in the case of a two sided Fresnel optic, i.e. a Moire Pattern is formed. In other words, interference of the light is caused by the superimposition of two regularly spaced patterns, causing light and dark rings.
The open Fresnel lens has further shortcomings which relate primarily to the medical aspects of such devices. Since the Fresnel surface may be placed in the sulcus of the eye or the capsular bag, the Fresnel surface is adjacent to the iris. The diameter of the iris, which is a variable opening in the eye, changes rapidaly as the ambient illumination changes. Under bright daylight conditions, the iris opening may be only a few millimeters, changing to wide open under darkened conditions. The action is entirely involuntary. The Fresnel surface in order to be effective must have sharp ridges at the juncture of individual lenticules. These, of course, could abrade the rear surface of the iris, causing inflammation. Also particulate pigment sheared from the iris or inflammatory cells may lodge in the grooves of the Fresnel, destroying its effectiveness.
The lens of the present invention overcomes the foregoing objections to a Fresnel lens plus adds some unique features not present in existing intraocular lenses of any type.
The lens of the present invention utilizes a Fresnel surface sealed from its immediate environment. Fresnel lenses are flat optical devices which focus light from a series of concentric grooves or lenticules which are molded or cut into a surface of the device. Each groove is trapezoidal in crosssection, with the face angles varied in a controlled manner at different distances from the optical axis of the lens. Specifically, the Fresnel elements are formed on one surface of the optical zone of the lens, and no large thickness is required. This is because the Fresnel elements perform the desired focusing action by acting as a series of concentric prisms, deviating the incoming light rays to a common point. This means that the lens of the prior invention, when made of flexible material, may be folded, rolled or otherwise deformed to an extremely small diameter for insertion into the eye through an extremely small incision.
Specifically, the lens of this invention has one flat or plano side, rather than being biconvex, because light is focused by means of a series of concentric grooves cut or molded into a surface of the lens, in accordance with Fresnel lens principles. Each groove formed in the surface of the lens is trapezoidal in cross-section, with the face angles of the successive grooves being varied in a controlled manner as a function of the distances of the respective grooves from the optical axis of the device.
Through computer controlled machinery, Fresnel lenses may be provided which are corrected for spherical aberration, reduce scatter and improve focusing efficiency. The combination of the sealed Fresnel surface on one side of the lens, with a flat plano surface or spherical surface on the opposite side, allows the intraocular lens of the invention to constitute an excellent replacement for the natural lens.
The sealed Fresnel surface can be applied to all materials with optical properties, including HEMA (hydrooxyethylmethylmetharylate). This is a hydrophilic material from which soft contact lenses are currently manufactured. The sealed Fresnel principle can be applied to the HEMA&lt;in its dehydrated state or after hydration. The lens may then be inserted into the eye in a dry, shrunken, small state or after hydration by deforming the surface.
The sealed Fresnel surface reduces reflection as compared to a conventional biconvex lens or plano convex lens, and there is less dispersion with the Fresnel surface lens. The Fresnel lenticules can be arranged to reduce spherical aberration.
The sealed Fresnel principle can be applied to all lens materials that are inserted inside the eye, including hard materials and heat sensitive hard materials that can be deformed and fixed outside the eye and which resume an optical shape after insertion into the eye, the heat of the aquaeous causing them to open and flatten.
However, there are certain problems which arise with respect to the Fresnel intraocular lens. For example, in order for the Fresnel lens to function properly it must have sharply shaped lenticules which often become a source of irritation when drawn across the surface of the iris. Frequently, the body's response to such irritation is to grow new tissue over the source of the irritation. This action ultimately destroys, or at least seriously reduces the effectiveness of the lens.
Another problem which arises is that the aqueous humor of the eye frequently contains particles which tend to lodge in the grooves of the Fresnel lens; and which tend to destroy the Fresnel surface or at least adversely affect its optical efficiency.
Accordingly, an object of the present invention is to provide a Fresnel type intraocular lens which has all the advantages of the prior art lenses but which is constructed so that the Fresnel surface itself is sealed to overcome the problems encountered by the prior art lenses.